Traffic-actuated control system



g- 26, 1969 P. c. BROCKETT TRAFFIC-ACTUATED CONTROL SYSTEM 2 Sheets-Sheet 1 Filed Jan. 6, 1967 FIG. I

FIG. 3

ATTORNEY United States Patent 3,464,059 TRAFFIC-ACTUATED CONTROL SYSTEM Peter C. Brockett, Milford, Conn., assignor to Laboratory for Electronics, Inc., Waltham, Mass, a corporation of Delaware Filed Jan. 6, 1967, Ser. No. 607,811 Int. Cl. (208g 1/02, 1/08 US. Cl. 340-37 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention pertains to a trafiic-actuated intersection right-of-Way control system. More particularly, this invention pertains to a trailic-actuated intersection control system which provides a fixed duration minimum initial interval concurrently with an initial interval having a duration dependent upon the number of vehicles waiting at the intersection for the right-of-way, so that, once right-ofway is transferred to the waiting vehicles, the initial interval of the right-of-way period does not end Jntil both the minimum initial interval and the variable initial interval have ended.

The right-of-way at numerous trafiic intersections is controlled by trafiic signal lights which respond to signals generated by trafiic-actu ated controllers. These trafiicactuated controllers include vehicle detectors for determining when and how many vehicles have approached an intersection on the street or traflic phase which does not have right-of-way. Once the vehicle detector has detected such a vehicle, the controller is initiated so that ultimately it gives the right-of-way to the street or highway on which one or more vehicles are waiting.

The right-of-Way period for a traffic phase is frequently divided into two or more intervals. The first of these is termed the initial interval of the right-of-way period. When right-of-way is transferred to a traffic phase in response to a signal from a tratfic-actuated control system, one or more vehicles will have already passed the vehicle detector and will be waiting between the detector and the intersection. The initial interval of the right-of-way period is provided to allow these waiting vehicles to cross the intersection once right-of-way is transferred to their phase. Cars passing the detector after right-of-way has been transferred to their phase do not cross the intersection during the initial interval; instead they cross during a subsequent time, frequently termed a vehicle or passage interval.

At the time right-of-way is transferred, only one car may be waiting at the intersection. Alternatively, several cars may be waiting between the detector and the intersection at the time right-of-w-ay is transferred. Accordingly, the traffic control system must provide an initial interval which is long enough to allow intersection-clearance time for the maximum number of vehicles which may be waiting between the detector and the intersection.

3,464,059 Patented Aug. 26, 1969 However, most etficient allocation of right-of-way requires that when only one vehicle is waiting at the intersection, the traflic control system must provide an initial interval of a short duration.

The length of time required for the waiting vehicles to cross the intersection is not directly proportional to the number of waiting vehicles. The first vehicle must start from rest after right-of-way is transferred to its phase and must then move through the intersection. The second vehicle starts from its rest position while the first vehicle is still in the intersection, and so it moves more rapidly through the intersection. Similarly, the remaining vehicles do not require as much additional time as do the first one or two vehicles. Thus, for maximum efiiciency and minimum trafiic congestion, the traffic control system must provide an initial interval which is variable between a minimum duration, sufficient to allow one or two cars to pass the intersection, and a maximum duration, sufficient to allow the maximum number of cars to pass. The traffic control system should vary the duration of the initial interval in accordance with the number of vehicles which have passed the detector prior to the transfer of right-of-way, but it should not cause it to be directly proportional to the number of waiting vehicles.

There are available traffic control systems having circuits for providing a variable initial interval of the rightof-way perod. These existing control systems utilize initial interval circuits having a first timer which provides the minimum initial interval and a second timer which provides additional periods of time of a duration dependent upon the number of vehicles which have passed the detector prior to the transfer of right-of-way. This sequential timing requires that the second timer be capable of timing a very brief period to be added to the minimum initial interval of the first timer. Since this added period is so short, it is difi'icult to adjust the second timer accurately, and components within the second timer must be selected with close tolerances. Such control systems are therefore expensive. Many of these control systems which utilize two sequential timers activate the second timer for a period of time dependent upon the total duration of the vehicle detection signals which have been received prior to transfer of right-of-way. However, in addition to being dependent upon the number of vehicles passing the detector, this total time duration may vary due to such factors as the speed at which the vehicles pass the detector, the length of the vehicles, the size wheels on the vehicles, etc. In addition, in such a control system the minimum initial interval of the first timer is long enough to permit, for example, two or three vehicles to cross the intersection, as selected by the highway engineer. But as these first vehicles pass the detector, they activate the second timer, and so the initial interval is unnecessarily lengthened by the Second timer. This problem can be overcome by providing within the initial interval circuit counters and switches to count a minimum number of vehicles and then to switch the second timer into the circuit. However, such counting and switching circuitry is complex and expensive, and so it increases the possibility of a malfunction within the trafiic control system, as well as adding to its cost.

SUMMARY OF THE INVENTION The present invention is a traflic-actuated intersection right-of-way control system having an initial interval circuit in which a small controlled alteration is made in a stored voltage each time a vehicle is detected approaching the intersection on a traffic phase which does not ha e right-of-way. During the initial interval after right-of-Way is transferred to that street or phase, an interval timer circuit w thin the control system times the minimum initial interval, and a variable timer circuit times an interval with a duration dependent upon the amount by which the stored voltage has been altered. Since this voltage alteration is controlled, it is not subject to inaccuracies due to such things as the speed, length, and wheel size of the waiting vehicles. This variable timer circuit operates concurrently with the minimum initial interval timer circuit. Therefore, if only one or two vehicles are waiting for the right-of-way, the variable timer will complete its timing before the minimum timer; out if a large number of vehicles is waiting for the rightof-way, then the minimum timer completes its timing first. When both the minimum timer and the variable timer have completed their timing, the control syst m steps the right-of-way period to the next interval in its sequence.

It is accordingly an object of the present invention to provide an improved traffic-actuated intersection rightof-way controller.

It is another object of the present invention to provide a traific-actuated intersection controller having an initial interval timing circuit which permits the timing of an initial interval adjusted according to the number of cars waiting for the right-of-way beyond a pre-set minimum number, without the requirement of complex counting and switching circuitry.

It is a further object of the present invention to provide a traffic actuated intersection controller having an initial interval timing circuit in which a minimum time period and a variable time period determined by the number of vehicles awaiting right-of-way are concurrently timed and jointly determine the duration of the initial interval.

It is still another object of the present invention to provide a trafiic-actuated intersection right-of-way control system having an initial interval circuit which provides an initial interval that is adjusted in accordance withthe number of vehicles waiting for the right-of-way, beyond a pre-set minimum number, and which is free frominaccuracies due to variations in vehicle characteristics, such as speed, length, and wheel size.

These and other objects and advantages of the present invention will be apparent from the following detailed description and claims when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a plan view of a street intersection at which the right-of-way is controlled by a traffic-actuated control system.

FIGURE 2 is a block diagram of a trafiic-actuated control system including both a minimum initial interval timer and a variable initial interval timer which operate concurrently.

FIGURE 3 depicts waveforms at various points in the circuit of FIGURE 2 and is useful in explaining the operation of the control system.

DESCRIPTION OF A PREFERRED EMBODIMENT FIGURE 1 depicts a street intersection which may be controlled by means of a traffic-actuated control system including a variable initial interval circuit and incorporating the present invention. In FIGURE 1 the north-south street will be referred to as phase A and the east-west street as phase B. Signal controls the right-of-way between phases A and B. Vehicle detectors 12 and 14 detect the northbound and southbound trafiic, respectively, in phase A, and each vehicle passing either detector 12 or detector 14 causes a pulse to be transmitted via line 16 to the traflic-actuated control system 18 mounted with a terminal box at the side of one of the streets. Similarly, detectors 20 and 22 monitor the eastbound and westbound phase B traflic, respectively, and they are connected via line 24 to the control system 18. The control system 18 is connected by line 25 to signal 10 to control the rightof-way between phases A and B. Detectors 12, 14, 20, and 22 may be any of a number of types. For example, each may be an overhead detector of a radar or sonic 4 type. Alternatively, they may be embedded in the roadway, in which case they may be inductive loop, magnetic, or treadle detectors, for example. It is only necessary that each detector generate an electrical signal upon the passage of a vehicle which signal can be converted to a pulse.

FIGURE 2 depicts in block diagram form the circuitry of tralfic-actuated control system 18 which is made up of interval sequencing and memory unit 26, interval timer 28, and the variable initial interval timer. Lines 16 and 24 from the phase A and phase B detectors and line 25 to the signal 10 connect to unit 26. Unit 26 and timer 28 are connected together by a plurality of lines, represented in FIGURE 2 by line 29. The interval sequencing and memory unit 26 and the interval timer 28 can be of any standard design, and together they may form a trafficactuated control system having a fixed initial interval.

Unit 26 steps the control system 18 output on line 25 in accordance with its programmed memory. Timer 28 includes circuitry to time the various intervals which make up the interval sequence. There is a line 29 corresponding to each interval of the right-of-way sequence, as well as a line 29 for other necessary control signals to timer 28. At each interval of the sequence unit 26 applies a signal via a corresponding line 29 to timer 28 to initiate the timing of that interval. At the end of the appropriate time, timer 28 generates a control signal which is utilized to cause unit 26 to step to the next interval in the sequence. A manual control (not shown) for each interval of the sequence is supplied on either unit 26 or timer 28 to set the duration of each interval which is not varied in accordance with signals from the phase A and phase B vehicle detectors. Thus, both the phase A and the phase B minimum initial interval are set by means of these manual controls. United States Patent No. 3,267,- 424, issued Aug. 16, 1966, to P. C. Brockett et al., and assigned to the same assignee as the present invention, discloses and claims a trafi'ic-actuated control system with a fixed initial interval which is suitable for use as interval sequencing and memory unit 26 and interval timer 28. For example, in FIGURE 1 of Patent No. 3,267,424, normal interval time circuit corresponds to interval timer 28 of the present invention as shown in FIGURE 2. The remainder of FIGURE 1 of Patent No. 3,267,424 corresponds to interval sequencing and memory unit 26 of the present invention. AND gate 210 of the present invention is inserted into line 141 in FIGURE 1 of Patent No. 3,267,424, so that lines 214 and 216 of the present invention correspond to line 141 of that patent. The variable initial interval circuitry forming a part of the present invention (components 32-210 of FIGURE 2) is then added to the circuitry of FIGURE 1 of Patent 3,267,424.

Each vehicle passing over detector 12 or 14 in the phase A lanes causes a phase A detection pulse which is applied from interval sequencing and memory circuit 26 to low-pass filter 30 via line 32. The output from lowpass filter 30 is connected to the signal input of IN- I-IIBITED-AND gate 34 which has its output tied to the input of mono-stable multivibrator or one-shot 36. The output of one-shot 36 is connected to the cathode of diode 38, which has its anode connected through rheostat 40 to junction 42. Junction 42 is tied to the input of phase A storage unit or storage means 44, which, for example, may be a storage capacitor. 1

When phase A does not have the right-of-way, the first vehicle passing either phase A detector 12 or 14 initiates a continuing signal A CALL, in addition to causing a detection pulse on line 32. The A CALL signal signifies that a vehicle has passed a phase A detector to call the right-of-way to phase A. This A CALL signal is applied by line 46 from interval sequencing and memory unit 26 to the first inhibit input of INHIBITED-AND gate 48, the output of which connects through rheostat 50 .to line 51 which ties it to junction 42. During the phase A initial interval, immediately after right-of-way is transferred to phase A, the signal AI is applied, by line 52 from unit 26 to the inhibit input otINHIBITED-AND gate 34 and to the second inhibit input of INHIBITED-AND gate 48. The signal input of INHIBITED-AND gate 48 is tied to a suitable source of potential such as first voltage source V1. Line 52 also applies the AI signal to the first input of AND gate 54, which has its output connected through rheostat 56 to line 51 which ties it to junction 42.

Circuitry identical to that just described for phase A is also provided for phase B. Thus, each vehicle passing detector 20 or detector 22 generatesa signal over line 24 to cause a phase B detection pulse to be applied from in: terval sequencing and memoryunit 26 to low-pass filter 130 via line 132. The output of low-pass filter 130 is connected to the signal input of INHIBITED-AND gate 134. The output of INHIBITED-AND gate 134 is connected to the input of one-shot multivibrator 136, which has its output connected to the cathode of diode 138. The anode of diode 138 connects through rheostat 140 to junction 142. Junction 142 is connected to the input of the phase B storage unit or storage means 144, which again may be a storage capacitor, for example.

The first vehicle to pass either phase B detector 20 or 22 during the time that phase B does not have right-ofway initiates a continuing B CALL signal which is applied by line 146 from interval sequencing and memory unit 26 to the first inhibit input of INHIBITED-AND gate 148. INHIBITED-AND gate 148 has its output connected through rheostat 150 to line 151 which ties to junction 142.

During the phase B initial interval, immediately after right-of-way is transferred to phase B, the signal BI is applied by line 152 from unit 26 to the inhibit input of INHIBITED-AND gate 134 and to the second inhibit input of INHIBITED-AND gate 148. The signal input of INHIBITED-AND gate 148 is tied to first voltage source V1. Line 152 also applies the BI signal to the first input of AND gate 154, which has its output coupled through rheostat 156 to line 151 which ties it to junction 142.

Junctions 42 and 142 are connected to the two inputs of OR gate 202. The output of OR gate 202 is connected to the first input of AND gate 204 which has its output tied to the input of Schmitt trigger 206. The output of Schmitt trigger 206 is connected to the set input of flipflop 208, which has its set output connected to the first input of AND gate 210 and its reset output tied to the second input of AND gate 204. The reset output of flipfiop 208 is also connected to the second inputs of AND gates 54 and 154, both of which have their third inputs tied to a suitable source of potential such as second voltage source V2.

The AI and BI signals are applied by lines52 and 152 respectively, to the two inputs of OR gate 212. The output of OR gate 212 is connected to the reset input of flip-flop 208. The second input of AND gate 210 is connected via line 214 to the output of interval timer 28. AND gate 210 has its output connected via line 216 to circuitry within interval sequencing and memory unit 26 which steps the right-of-way sequence to its next interval when an electrical signal is applied via line 216.

OPERATION OF THIS PREFERRED EMBODIMENT When the right-of-way is on the phase B street and no vehicle has passed either detector 12 or detector 14 to call the right-of-way to the phase A street, the phase A circuitry (components 30 through 56 in FIGURE 2) is in its quiescent condition, and no signal is applied to the phase A circuitry by lines 32, 46 and 52 from interval sequencing and memory unit 26. If right-of-way has been on phase B for enough time that it is no longer in its initial interval, then flip-flop 208 is in its set condition. INHIBITED-AND gates 34 and 48 are enabled, since no inhibiting inputs are applied to them on lines 46 and 52. AND gate 54 is blocked since there are no signals applied to its first or second inputs. In addition, one-shot 36 is in its stable state, which means that its output, applied to diode 38, is at a high voltage level in the embodiment depicted in FIGURE 2 in which V1 and V2 are both sources of positive potential. This high voltage from oneshot 36 is blocked from voltage storage unit 44 by diode 38. The voltage on voltage storage unit 44 is at the level of the voltage from first source VI, which is adjusted to be just below the firing level of Schmitt trigger 206. FIGURE 3(a) depicts the voltage on the phase A voltage storage means 44, and in the quiescent condition this voltage is shown at level 70.

When a vehicle passes detector 12 or detector 14, a phase A detection pulse is applied by line 32 from unit 26 to low-pass filter 30. FIGURE 3(b) depicts the phase A detection pulses on line 32, and this phase A detection pulse from the first vehicle is shown as pulse 72. In addition to causing detection pulse 72, the first vehicle to pass a phase A detector during the time that phase A does not have right-of-way results in interval sequencing and memory unit 26 generating a continuing signal A CALL which is applied by line 46 to the first inhibit input of INHIBIT- ED-AND gate 48. INHIBITED-AND gate 48 then open circuits rheostat 50, and so the phase A storage unit 44 is isolated from the first voltage source V1.

The phase A detection pulse 72 passes through IN- HIBITED-AND gate 34 to trigger one-shot multivibrator 36. As a consequence, the one-shot assumes its unstable state in which its output drops to a low value, as shown by a pulse 74 of FIGURE 3(0). The duration of pulse 74 is dependent solely upon the characteristics of oneshot 36, and so each pulse from one-shot 36 is of the same duration, as shown in FIGURE 3(c), even if the duration of the detection pulses varies, as shown in FIGURE 3(b), due to variation in vehicle speed, length, the tire size, etc. When one-shot 36 is in its unstable state, a measured amount of voltage is passed from the phase A storage unit 44 through rheostat 40 and diode 38 to the one-shot 36, and so the voltage on storage unit 44 drops to level 76, shown in FIGURE 3(a). Each subsequent vehicle passing either phase A detector 12 or 14 causes a phase A detec tion pulse on line 32, such as pulses 78. Each of these pulses 78 triggers one-shot 36 to its unstable state, as shown by pulses 80 in FIGURE 3( b), and so a controlled amount of voltage is removed from storage unit 44, dropping its voltage a fixed amount, as indicated at points 82 in FIGURE 3(a). The amount of voltage removed from a storage unit 44 at each phase A detection pulse is controlled by the length of time which one-shot 36 remains in its unstable state and by the setting of rheostat 40.

When right-of-way is transferred to the phase A street, the A CALL signal is terminated, and the AI signal, depicted as pulse 84 in FIGURE 3(d), is applied on line 52 to inhibit INHIBITED-AND gate 34 from passing any additional phase A detection pulses. Consequently, detection pulses, such as pulse 86, initiated by vehicles passing a phase A detector after right-of-way has been transferred to phase A, have no effect on the duration of the initial interval. The AI signal on line 52 inhibits IN- HIBITED-AND gate 48, and so phase A storage unit 44 remains isolated from first voltage source V1, even though the A CALL signal on line 46 has been terminated. The A CALL signal is not initiated again by vehicles passing phase A detector 12 or 14, so long as phase A has rightof-way.

The AI signal passes through OR gate 212 to reset fiipflop 208. The reset output of flip-flop 208 is applied to the firing level of Schmitt trigger 206, depicted as level 88 in FIGURE 3(a), the Schmitt trigger applies a pulse to the set input of flip-flop 208. This removes the enabling inputs applied by the reset output of flip-flop 208 to AND gates 54 and 204. The set output of flip-flop 203 is applied to the first input of AND gate 210.

The length of time required for the voltage on the phase A voltage storage unit 44 to reach the firing level 88 of Schmitt trigger 206 is dependent upon the level 90 of the voltage on storage unit 44 just prior to the transfer of right-of-way to the phase A street to generate the phase A initial interval. The level 90, in turn is dependent upon the number of vehicles which have passed the phase A detectors 12 and 14 to trigger one-shot 36 so that a controlled amount of voltage is removed from storage unit 44. The period of time is, of course, also dependent upo the setting of rheostats 4 and 56 and the magnitude of the voltage from voltage source V2. For a'given value of voltage from source V2 and given settings of rheostats 40 and 56, the length of time which elapses between the start of the phase A initial interval and the generation of the output pulse from Schmitt trigger 206 is dependent upon the number of phase A detection pulses which have been applied to line 32.

When flip-flop 208 assumes its set condition, it applies voltage to the first input of AND gate 210. When interval timer 28 has completed timing the minimum initial interval, it applies voltage via line 214 to the second input of AND gate 210. Thus, if the number of cars which have passed the phase A detectors 12 and 14 prior to the transfer of right-of-way is so small that they all can cross the intersection during the minimum initial interval, the variable initial interval timer applies voltage to the first input of AND gate 210 before interval timer 28 applies voltage to the second input of the gate. Consequently, as soon as interval timer 28 indicates the end of the minimum initial interval, the coincidence of inputs to AND gate 210 causes gate 210 to apply a control signal via line 216 to interval sequencing and memory unit 26 to cause the end of the initial interval and the commencement of the next interval, which may be the vehicle or passage interval, for

example. However, it several vehicles are waiting for the phase A right-of-way, it takes longer for the voltage on the phase A storage unit 44 to build up to the firing level of Schmitt trigger 206. In such a case, interval timer 28 applies voltage via line 214 to the second inputof AND gate 210, marking the end of the minimum initial interval, before Schmitt trigger 206 fires, setting flip-flop 208 to apply voltage to the first input of AND gate 210. Consequently, there is no output on line 216 from AND gate 210 until this longer variable time has passed, and the initial interval lasts longer to allow all the waiting vehicles to cross the intersection. When the phase A initial interval ends, the AI signal on line 52 terminates.

When flip-flop 208 turns to its set condition, the enabling input is removed from AND gates 54 and 204. Consequently, Schmitt trigger 206 shuts off, and phase A voltage storage unit 44 is isolated from the second voltage source V2. Termination of the AI signal removes the inhibiting input from lNHIBITED-AND gates 34 and 48. Therefore, voltage from first voltage source V1 is applied to the phase A voltage storage unit 44 to return it to its initial level 70 as shown in FIGURE 3(a). Since the A CALL signal is not initiated during the time right-of-way is on phase A, INHIBITED-AND gate 48 does not isolate phase A storage unit 44 from first voltage source V1 during this time.

In order to fire Schmitt trigger 206, the voltage on storage unit 44 must be at a value 88, slightly greater than the quiescent value 70. Consequently, the voltage from second voltage source V2 must be slightly greater than the voltage from first voltage source V1. After Schmitt trigger 206 fires to end the initial interval, IN- HIBITED-AND gate 48 again applies voltage source V1 to the phase A voltage storage unit 44. Since the volt- 8 age level 88 on storage unit 44 is slightly greater than the voltage level from source V1, voltage is then drained from the storage unit 44. Voltage source V1 clamps the storage unit 44 at voltage level 70 so that no voltage can leak from the storage unit to drop this voltage to a lower level during the quiescent condition. Phase A detection pulses occurring after the end of the phase A initial interval but during the time that rightof-way is on phase'A are passed by INHIBITED-AND gate 34 and trigger one-shot 36. Thus, detection pulse 92, shown in FIGURE 3(1)), causes negative pulse 94 of FIGURE 3(a) from one-shot 36. The drop in voltage at the output of one-shot 36 causes ripple 96, shown in FIGURE 3(a), in the voltage stored in storage unit 44, but source V1 again brings the stored voltage to level 70.

After the phase A initial interval has ended, flip-flop 208 .remains in its set condition until the next initial interval signal from unit 26 passes through OR gate 212 to reset flp-flop' 208. During this period of time, the set output from flip-flop 208 enables AND gate 210 to pass further signals on line 214 from interval timer 28 to line 216 which connects to interval sequencing and memory unit 26. Thus, signals from interval timer 28 marking the termination of other intervals in the timing sequence of the right-of-way period are not blocked by AND gate 210. AND gate 210 is blocked only while the variable initial interval circuit is timing.

Operaton of the phase B variable initial interval timing circuitry is the same as that just described for phase A. Interval sequencing and memory unit 26 applies as inputs to the phase B circuitry (components through 156 in FIGURE 2), the phase B detection pulses, and the signals BI, and B CALL. The voltage on phase B storage unit 144 passes through OR gate 202 and AND gate 204 to Schmitt trigger 206, just as does the voltage from phase A storage unit 44.

Each vehicle passing either phase A detector 12 or phase A detector 14 will cause the voltage on phase A storage unit 44 to be altered by a slight amount and will lengthen the variable initial interval. Since the phase A circuitry is not able to distinguish between vehicles passing detector 12 and vehicles passing detector 14, the voltage on storage unit 44 is altered by the same amount when two northbound vehicles are waiting between detector 12 and the intersection as it is when one northbound vehicle and one southbound vehicle are waiting between detectors 12 and 14, respectively, and the intersection. Thus, the variable initial interval will be of the same duration for two vehicles waiting in the same direction as it is one vehicle waiting in each direction. However, adjustments can be made via the rheostats 40 and 56 by the highway engineer to vary the effect which each waiting vehicle has on the variable initial interval to meet the requirements of each individual intersection. Thus, for example, if tratfic engineering studies show that at a given intersection approximately 60% of the phase A traflic is northbound, then rheostats 40 and 56 can be adjusted so that each phase A detection pulse results in 60% of the necessary alteration in the initial interval. The particular adjustments made for a given intersection will be ,dependent upon traflic flow at that intersection.

While the above description is with reference to an intersection having two interfering tratfic phases, it will be obvious that the traific-actuated right-of-way control system of the present invention can be utilized at intersections having a greater number of interfering vehicle phases by utilizing an appropriate interval sequencing and memory unit 26 and an appropriate interval timer 28 to accommodate the desired number of phases and by including within the variable initial interval timer sets of phase-handling circuitry (e.g., components 30-56 utilized for phase A in FIGURE 2) for the deisred number of phases. Similarly, it can be utilized on a single phase of an intersection controlled by a semi-actuated control system. The term multiphase trafiic intersection thus describes all of these types of intersections.

In the above ,detailed description V1 and V2 have been sources of positive voltage and the one-shot 36 output has been a high voltage in the stable state and a low voltage in the unstable state. By appropriate selection of components, either V1 or V2 could be ground potential. Alternatively, in the quiescent condition a low voltage level could be on storage unit 44, with a controlled amount of voltage added to storage unit 44 from oneshot 36 each time a vehicle passes a detector. Additionally, gating has been provided by AND, OR and INHIBITED-AND gates, but other types of gates, for example, NOR and NAND gates could be utilized.

While in the above detailed description, each vehicle passing the phase A detector has altered the voltage stored on phase A storage unit 44 to lengthen the duration of the variable initial interval, flexibility can be achieved by making the detection pulse from the first vehicle to pass a phase A detector have no efiect on the stored voltage. This can be easily accomplished by the simple method of inhibiting INHIBITED-AND gate 34 in the absence of the A CALL signal. Thus, for example, the A CALL signal on line 46 can be delayed and applied to another signal input (not shown) on IN- HIBITED-AND gate 34. Since the A CALL signal is not present prior to the first detection pulse, gate 34 will be blocked to this first pulse. Subsequent detection pulses will pass through gate 34, since the A CALL will enable the gate. In such a case, pulses occurring after termination of the A CALL signal, when phase A has right-ofway (e.g., pulses 86 and 92), will not trigger one-shot 36. Thus, flexibility can be achieved without complex switching and counting circuitry.

Thus, among others, the several objects of the invention as specifically aforc-noted are achieved.

I claim:

1. A multiphase trafiic intersection right-of-way control system for providing to a trafiic phase in response to traflic-actuated signals a right-of-way period including an initial interval and at least one other interval, said control system comprising in combination:

(A) detection means for generating detection signals in response to vehicles approaching an intersection on a trafiic phase which does not have right-of-way;

(B) apparatus means coupled to said detection means for receiving said detection signals and for sequentially stepping through prescribed intervals in response to control signals to bring right-of-way to said traflic phase, said apparatus generating for each trafiic phase (1) a detection pulse in response to each received detection signal for said traflic phase, (2) a continuing signal indicating that at least one detection signal has been received for said trafiic phase when said traffic phase does not have right-of-way, and (3) an initial interval signal during the initial interval of right-of-way on said trafiic phase;

(C) an interval timer connected to said apparatus to receive therefrom signals indicative of initiation of each interval of each right-of-way period and, after timing the appropriate interval, to generate a control signal;

(D) a variable initial interval timer including (1) a set of phase circuitry for each trafiic phase of said intersection comprising (a) voltage storage means,

(b) first means coupled to said apparatus and to said voltage storage means and adapted for connection to a first voltage source to apply voltage from said first voltage source to said voltage storage means in the absence of both said continuing signal and said initial interval signal for said traffic phase,

(c) second means coupled to said apparatus and to said voltage storage means to alter in a controlled manner stored voltage on said voltage storage means in response to each of said detection pulses for said trafiic phase occurring in the absence of said initial interval signal for said trafiic phase,

(d) third means coupled to said apparatus and to said voltage storage means and adapted for connection to a second voltage source to apply voltage from said second voltage source to said voltage storage means when said initial interval signal is present for said traffic phase, the voltage from said second voltage source being of a magnitude different from the magnitude of the voltage from said first voltage source,

(e) said second means adapted to alter said stored voltage to cause the voltage difference between said altered stored voltage and the voltage from said second voltage source to be greater than the voltage difference between the voltage from said first voltage source and the voltage from said second voltage source;

(2) pulse generating means having an input coupled to the voltage storage means of each trafiic phase, said pulse generating means generating a signal when there is applied to its input a voltage having a magnitude between the magnitudes of the voltages of said first and second voltage sources;

(E) switching means connected to said apparatus, to said interval timer, and to said pulse generating means and capable of assuming first and second stable states, said switching means assuming said first stable state when said pulse generating means initiates a signal and assuming said second stable state upon initiation of an initial interval signal for any trafiic phase, said switching means applying said control signal to said apparatus when said switching means is in its first stable state to cause sequential stepping through the prescribed intervals of right-of-way periods.

2. A multiphase trafiic intersection right-of-way control system for providing to a traffic phase in response to trafiic-actuated signals a right-of-way period including an initial interval and at least one other interval, said control system comprising in combination:

(A) apparatus means for receiving detection signals indicative of vehicles approaching an intersection on a trafiic phase which does not have right-of-way and for sequentially stepping through prescribed intervals in response to control signals to bring right-of-way to said traffic phase, said apparatus generating for each trafiic phase (1) a detection pulse in response to each received detection signal for said traffic phase,

(2) a continuing signal indicating that at least one detection signal has been received for said traffic phase when that traflic phase does not have right-of-way, and

(3) an initial interval signal during the initial interval of right-of-way on said trafiic phase;

(B) an interval timer connected to said apparatus to receive therefrom signals indicating the initiation of each interval of each right-of-way period and, after timing the appropriate interval, to generate a control signal;

(C) a variable initial interval timer including (1) a set of phase circuitry for each traffic phase COlHPIISlIlg (a) voltage storage means,

(b) first means coupled to said apparatus and to said voltage storage means and adapted for connection to a first voltage source to apply voltage from said first voltage source to said voltage storage means in the absence of both said continuing signal and said initial interval signal for said trafiic phase,

(c) second means coupled to said apparatus and to said voltage storage means to alter in a controlled manner stored voltage on said voltage storage means in response to each of said detection pulses for said traflic phase occurring in the absence of said initial interval signal for said traflic phase,

(d) third means coupled to said apparatus and to said voltage storage means and adapted for connection to a second voltage source to apply voltage from said second voltage source to said voltage storage means when said initial interval signal is present for said trafiic phase, the voltage from said second voltage source being of a magnitude different from the magnitude of the voltage from said first voltage source,

(e) said second means adapted to alter said stored voltage to cause the voltage difference between said altered stored voltage and the voltage from said second voltage source to be greater than the voltage difference between the voltage from said first voltage source and the voltage from said second voltage source;

(2) pulse generating means having an input coupled to the voltage storage means of eachtratfic phase, said pulse generating means providing a signal when there is applied to its input a voltage having a magnitude between the magnitudes of the voltages of said first and second voltage sources;

(D) switching means connected to said apparatus, to said interval timer, and to said pulse generating means and capable of assuming first and second stable states, said switching means assuming said first stable state when said pulse generating means initiates a signal and assuming said second stable state upon initiation of an initial interval signal for any traflic phase, said switching means applying said control signal to said apparatus when said switching means is in its first stable state to cause sequential stepping through the prescribed intervals of right-of-way periods.

3. A multiphase tralfic intersection right-of-way control system as claimed in claim 2 in which said second means includes a monostable multivibrator which is triggered to its unstable state in response to each of said detection pulses and which has its output coupled to said voltage storage means to alter in controlled manner voltage stored on said voltage storage means when said monostable multivibrator is in its unstable state.

4. A multiphase tratfic intersection right-of-way control system as claimed in claim 2 in which said switching means includes, a bistable multivibrator capable of assuming first and second stable states and includes gating means, said bistable multivibrator coupled to said pulse generating means and to said apparatus to cause said bistable multivibrator to assume its first stable state when said pulse generating means initiates a signal and to as sume its second stable state when an initial interval signal is initiated for any traffic phase, said gating means connected to said bistable multivibrator, to said interval timer, and to said apparatus to apply said control signal to said apparatus when said bistable multivibrator is in its first stable state to cause sequential stepping through the prescribed intervals of right-of-way periods.

5. A multiphase tratfic intersection right-of-way control system for providing to a traffic phase in response to traflic actuated signals a right-of-way period including 12 an initial interval and at least one other interval, said control system comprising in combination:

(A) apparatus means for receiving detection signals indicative of vehicles approaching an intersection on a traflic phase which does not have right-of-way and for sequentially stepping through prescribed intervals in response to control signals to bring rightof-way to said traffic phase, said apparatus generating for each trafiic phase V (1) a detection pulse in response to each received detection signal for said traffic phase,

(2) a continuing signal indicating that at least one detection signal has been received for said traffic phase when that trafiic phase does not have right-of-way, and

(3) an initial interval signal during the initial interval of right-of-way'on said 'traflic phase;

(B) an interval timer connected to said apparatus to receive therefrom signals indicative of initiation of each interval of each right-of-way period and, after timing the appropriate interval, to generate a control signal; i

(C) a set of phase circuitry for each trafiic phase and including (1) voltage storage means,

g (2) first gating means coupled to said apparatus and to said voltage storage means, and adapted for connection to a first voltage source to apply voltage from said first voltage source to said voltage storage means in the absence of both said continuing signal and said initial interval signal for said traflic phase,

(3) second gating means connected to said apparatus and to said voltage storage means, and adapted for connection to a second voltage source to apply voltage from said second voltage source to said voltage storage means when said initial interval signal is present for said traflic phase, the voltage from said second voltage source being of a magnitude different from the magnitude of the voltage from first voltage source;

(4) a monstable multivibrator having an input and an output,

(5) third gating means coupled to said apparatus and to said monostable multivibrator input to pass detection pulses from said apparatus to said input in the absence of said initial interval signal to cause said monostable multivibrator to assume its unstable state at the occurrence of each detection pulse,

('6) said monostable multivibrator output coupled to said voltage storage means to alter voltage stored on said voltage storage means so that the voltage ditference between said altered stored voltage and the voltage from said second voltage source is greater than the voltage difference between the voltage from said first voltage source and the voltage from said second voltage source;

(D) pulse generating means having an input coupled to the voltage storage means of each set of phase circuitry, said pulse generating means generating a signal when there is applied to its input a voltage having a magnitude between the magnitudes of the voltages of said first and second voltage sources;

(E) bistable multivibrator capable of assuming first and second stable states and connected to said pulse generating circuit to cause said bistable multivibrator to assume its first stable state when said pulse generating circuit initiates a signal, said bistable multivibrator coupled to said apparatus to cause said bistable multivibrator to assume its second stable state when an initial interval signal is initiated for any traffic phase;

(F) gating means connecting to said bistable multivibrator to said interval timer, and to said apparatus to apply said control signal to said apparatus when said bistable multivibrator is in its first stable state.

6. In a multiphase traific intersection right-of-way control system which provides to a traffic phase in response to traffic-actuated signals a right-of-way period including an initial interval and at least one other interval and which includes (A) apparatus for receiving detection signals indicative of vehicles approaching an intersection on a trafiic phase which does not have right-of-way and for sequentially stepping through prescribed intervals in response to control signals to bring right-ofway to said traffic phase, said apparatus generating for each trafiic phase (1) a detection pulse in response to each received detection signal for said trafiic phase,

(2) a continuing signal indicating that at least one detection signal has been received for said traffic phase when said traflic phase does not have right-of-way, and

(3) an initial interval signal during the initial interval of right-of-way on said traffic phase; and

(B) an interval timer connected to said apparatus to receive therefrom signals indicative of initiation of each interval of each right-of-way period and, after timing the appropriate interval, to generate a control signal;

the improvement comprising a variable initial interval timer including:

(A) a set of phase circuitry for each trafiic phase comprising (1) voltage storage means,

(2) first means coupled to said apparatus and to said voltage storage means and adapted for connection to a first voltage source to apply voltage from said first voltage source to said voltage storage means in the absence of both said continuing signal and said initial interval signal for said trafiic phase,

(3) second means coupled to said apparatus and to said voltage storage means to alter in a controlled manner stored voltage on said voltage storage means in response to each of said detection pulses for said trafiic phase occurring in the absence of said initial interval signal for said trafiic phase,

(4) third means coupled to said apparatus and to said voltage storage means and adapted for connection to a second voltage source to apply voltage from said second voltage source to said voltage storage means when said initial interval signal is present for said traflic phase, the voltage from said second voltage source being of a magnitude dilferent from the magnitude of the voltage from said first voltage source;

(5) said second means adapted to alter said stored voltage so that the voltage dilference between said altered stored voltage and the voltage from said, second voltage source is greater than the voltage difference between the voltage from said first voltage source and the voltage from said second voltage source;

(B) pulse generating means having an input coupled to the voltage storage means of each trafiic phase, said pulse generating means generating a signal when there is applied to its input a voltage having a magnitude between the magnitudes of the voltages of said first and second voltage sources;

(C) switching means connected to said apparatus, to said interval timer, and to said pulse generating means and capable of assuming first and second stable states, said switching means assuming said first stable state when said pulse generating means initiates a signal and assuming said second stable state upon initiation of an initial interval signal for any traffic phase, said switching means applying said control signal to said apparatus when said switching means is in its first stable state to cause sequential stepping through the prescribed intervals of right-of-way periods.

7. The improvement claimed in claim 6 in which said second means includes a monostable multivibrator which is triggered to its unstable state in response to each of said detection pulses and which has its output coupled to said voltage storage means to alter in controlled manner voltage stored on said voltage storage means when said monost-able multivibrator is in its unstable state.

8. The improvement claimed in claim 6 in which said switching means includes a bistable multivibrator capable of assuming first and second stable states and includes gating means, said bistable multivibrator coupled to said pulse generating means and to said apparatus to cause said bistable multivibrator to assume its first stable state when said pulse generating means initiates a signal and to assume its second stable state when an initial interval signal is initiated for any traffic phase, said gating means connected to said bistable multivibrator, to said internal timer, and to said apparatus to apply said control signal to said apparatus when said bistable multivibrator is in its first stable state to cause sequential stepping through the prescribed intervals of right-of-way periods.

9. A variable initial interval circuit for use with a multiphase traflic intersection right-of-way control system which provides to a traffic phase in response to trafiic actuated signals a right-of-way period including an initial interval and at least one other interval and which includes:

(A) apparatus means for receiving detection signals indicative of vehicles approaching an intersection on a traffic phase which does not have right-of-way and for sequentially stepping through prescribed intervals in response to a control signal to bring rightof-way to said trafiic phase, said apparatus generating for each traffic phase 1) a detection pulse in response to each received detection signal for said trafiic phase (2) a continuing signal indicating that at least one detection signal has been received for said trafiic phase when that traffic phase does not have right-of-way, and

(3) an initial interval signal during the initial interval of right-of-way on said trafiic phase;

(B) an interval timer connected to said apparatus to receive therefrom signals indicative of initiation of each interval of each right-of-way period and, after timing the appropriate interval, to generate a control signal;

said circuit comprising:

(A) a set of phase circuitry for each trafiic phase and including (1) voltage storage means,

(2) first gating means coupled to said voltage storage means and adapted for connection to said apparatus and to a first voltage source to apply voltage from said first voltage source to said voltage storage means, in the absence o both said continuing signal and said initial interval signal for each traffic phase,

(3) second gating means coupled to said voltage storage means and adapted for connection to said apparatus and to a second voltage source t apply voltage from said second voltage source to said voltage storage means when said initial interval signal is present for said traflic phase, the voltage from said second voltage source being of a magnitude difi'erent from the magnitude of the voltage from said first voltage source;

(4) a monostable multivibrator having an input and an output,

(5) third gating means coupled to said monostable multivibrator input and adapted for connection to said apparatus to pass detection pulses from said apparatus to said input in the absence of said initial interval signal to cause said monostable multivibrator to assume its unstable state at the occurrence of each detection pulse,

(6) said monostable multivibrator output coupled to said voltage storage means to alter voltage stored on said voltage storage means so that the voltage difference between said altered stored voltage and the voltage from said second voltage source is greater than the voltage dilference between the voltage from said first voltage source and the voltage from said second voltage source;

(B) pulse generating means having an input coupled to the voltage storage means of each set of Phase circuitry, said pulse generating means generating a signal when there is applied to its input a voltage having a magnitude between the magnitude of the JOHN ,W. CALDWELL, Primary Examiner CHARLES M. MARMELSTEIN, Assistant Examiner voltages of said first and second voltage sources;

(C) a bistable multivibrator capable of assuming first and second stable states and connected to said pulse generating circuit to cause said bistable multivibrator to assume its first stable state when said pulse generating circuit initiates a signal, said bistable multivibrator adapted for connection to said apparatus to cause said bistable multivibrator to assume its second stable state when an initial interval signal is initiated for any traffic phase;

(D) gating means connected to said bistable multivibrator and adapted for connection to said interval timer and to said apparatus to apply said control signal to said apparatus when said bistable multivibrtor is in its first stable state.

References Cited UNITED STATES PATENTS 3,414,877 12/1968 Cress et a1. 340-37 

